docs: def _format_numer(number_format, prefix='', suffix=''):
      """Format a number to a string."""
      @_surpress_formatting_errors
      def inner(v):
          if isinstance(v, Number):
              return ("{{}}{{:{}}}{{}}"
                      .format(number_format)
                      .format(prefix, v, suffix))
          else:
              raise TypeError("Numberic type required.")
      return inner